The recent development in the technologies of supercritical carbon dioxide (S-CO 2 ) has caused a remarkable change in the dyeing process in the textile industry. The conventional wet-dyeing process using water is being replaced with the dry-dyeing process using S-CO 2 . The uniform addition of coloring material is necessary for any dyeing process. In the case of the beam dyeing process, an equal distribution of the dye fluid through the porous beam has to be ensured in order to achieve an evenly distributed dyeing. The present study focuses on the fluid dynamics aspects of the S-CO 2 beam dyeing process in order to study the flow characteristics and thereby obtain performance improvement. Computational fluid dynamics analyses were carried out and the methodology is validated with experimental results from a previous study. The flow distribution of S-CO 2 through a porous beam is analyzed at different conditions, such as varying the operating pressure, mass flow rate and inlet temperature. The comparison of compressible and incompressible flow through beam dyeing is also discussed. The current study revealed that the increase in mass flow rate through the system leads to higher non-uniformity in distribution. The operating pressure and inlet temperature were found to significantly affect the flow distribution. The flow reversal condition showed a mass flow distribution opposite to that of the normal flow condition. The cyclic flow condition with periodic normal and the reversed flow condition provide better uniformity in distribution of the flow than the normal flow condition. The present results provide guidelines to improve the levelness of the dye distribution in the fabric material. Keywords supercritical carbon dioxide, beam dyeing, porous beam, level dyeing, coefficient of dischargeDyeing is the process of adding color to textile products, such as fibers, yarns and fabrics. Dyeing is an essential process in the textile industry and uniform dyeing over the material surface is one of the objectives of the dyeing process. Dyeing processes of textile materials are carried out by allowing dye fluid to flow thoroughly. During this process, dye molecules form a strong bond with the substrates. One of the widely used types of dyeing process is beam dyeing with water as the dyeing fluid. Dry-dyeing with supercritical carbon dioxide (S-CO 2 ) has more advantage than the wet-dyeing process from both economic and environmental perspectives. S-CO 2 dyeing simplifies the dyeing process compared with wet-dyeing by eliminating contaminated water discharges, reducing consumption, excluding drying, discarding chemical level agents and diminishing air emission. The development of S-CO 2 technologies has replaced the use of dyeing fluid from water to S-CO 2 .The S-CO 2 beam dyeing process is a state-of-the-art technology in the textile industry. The main components of the beam dyeing vessel are a porous beam, a dyeing vessel and associated pipe connections. Figure 1, a schematic of the sectioned view, illustrates the

Methods are reported for less computationally expensive and more accurate implementations of the direct simulation Monte Carlo (DSMC) method for the simulation of high speed gas flows over arbitrarily shaped bodies. A new particle-tracking algorithm with a saving of computational time of up to 10% is reported in which tracking of particles is done with the help of big triangles having vertices lying on the boundary curves. An algorithm has been developed to generate DSMC cells for collision and sampling that contain a prescribed number of molecules. This algorithm is able to generate over 90% cells having the optimum number of seven or eight molecules for simulating collisions. Sampling for macroscopic properties is done on dynamic cells that contain a number of particles varying spatially as a function of the local number density. A criterion for finding the number of particles in sampling cells is presented. This criterion has been found to result in accurate and fast simulation of two-dimensional hypersonic flows of argon over a wedge, and argon and nitrogen over a circular cylinder.

No abstract

No abstract

High speed flow past a blunt body generates a detached bow shock which leads to a high surface pressure and as a result the development of a high aerodynamic drag. One of the ways to reduce drag and heat flux is the employment of an aerospike. Flow under consideration occurs at rarefied conditions. In the present study, the flow around a blunted body fitted with an aerospike is analyzed using an open source Direct Simulation Monte Carlo (DSMC) code, called as dsmcFoam in OpenFOAM, at a high Mach number (M=6) at different length to diameter ratios (L/D = 1.5, 2) at an angle of attack 0 o. The aerospike replaces the strong detached shock wave ahead of the body with a system of weaker oblique shock waves. A recirculating flow zone is developed between the shock and the blunt body, which acts like a streamlined profile, thus reducing the drag and wall heat flux. Reducing the aerodynamic drag ensures reaching the desired range or altitude, reduces the fuel usage, simplify the propulsion system requirements and maximize the ratio of payload to take off gross weight.